Method for preventing coke obstructions in pyrolysis plants

ABSTRACT

A method for the prevention of coke obstruction in a pyrolysis plant, for example in the cracking of ethane in the manufacture of ethylene, wherein cracked gases from a pyrolysis furnace at a temperature of 750* to 850*C. are passed to a cooler, and a screen is disposed in the inlet portion of the cooler at an easily accessible portion whereby the on stream time of the pyrolysis system is extended.

United States Patent Schneider et a].

[4 1 Apr. 29 1975 METHOD FOR PREVENTING COKE OBSTRUCTIONS IN PYROLYSIS PLANTS Inventors: Hans Schneider, near Heide, Holst;

Richard Gustav l-lussner, Heide. Holst; Raimund Erhard Fischer, Hemmingstedt, all of Germany Assignee: Deutsche Texaco Aktiengesellschait,

Hamburg, Germany Filed: June 11, 1973 Appl. No.: 369,048

Related U.S. Application Data Division of Set. No. 94 734, Dec. 3. I970. Pat. No. 377L638.

U.S. Cl. 55/97 Int. Cl Bold 46/00 Field of Search l96/98; 55/1, 267, 268.

55/DlG. 20, 269. 307, 308. 97. 385, 318, 320, 32l, 323, 331. 332, 333. 334, 335, 336, 463, 368; 202/96, 152, 163, 180. I82, 185.

[56] 4 References Cited UNITED STATES PATENTS 367,413 8/1887 Koch 55/308 X Primary Examiner-Bernard Nozick Attorney. Agent or Firn't-T. H. Whaley; C. G. Ries; Theron H. Nichols 57 ABSTRACT 5 Claims, 1 Drawing Figure l l v i.A I I rap/vac; l

a lk illl\\- Iii-1k F ITH M Ill mm {1 man: I

METHOD FOR PREVENTING COKE OBSTRUCTIONS IN PYROLYSIS PLANTS This is a division of application Ser. No. 94,734, filed Dec. 3, 1970, now U.S. Pat; 'No. 3,771,638.

BACKGROUND OF THE INVENTION In the known processes the hot olefin-containing cracked gases leaving the pyrolysis furnace are passed through a cooler and/or a quenching zone. The pyrolysed gases form coke inside the cooler, which is then separated. At the inlet of the heat exchanger surfaces of the cooler and on said surfaces the coke deposits in a firm crustlike layer or coating continuously increasing in thickness, which results in an ever reduced heat exchange, eventual obstructions and close-down of the plant. It is difficult and costly to remove these coke crusts, as the customary coolers have large heat exchange surfaces arranged over a minimum space.

There are tests known by which to obviate coke crust formation by measures derived from flow technique. This involves cooler inlets being equipped with devices whereby the rate of flow of the cracked gases is kept constant across the section of the cooler. Without these devices the coke crust formation used to be irregular across the section of the cooler, i.e. certain areas in the cooler were covered much faster by coke crusts than were others. With these devices coke crust formation proceeded at an equal rate across the section of the cooler, however, the times needed for covering certain parts of the cooler were slightly prolonged. Thus the close-down of the cooler was, not prevented, but delayed.

SUMMARY OF THE INVENTION The present invention relates to an improvement of methods for the recovery of olefins from saturated hydrocarbons by means of pyrolysis. It further relates to any other method for pyrolysing organic compounds in the gaseous phase, in which separation of coke is to be expected.

It is an object of this invention to prevent or considerably delay coke obstruction of the cooler, in order to extend many times the running times of the furnaces. It is another object of this invention to prevent coke obstruction of other parts of pyrolysis plants.

The present invention has solved these problems by a method for preventing coke obstructions in pyrolysis plants, characterized by causing the coke to deposit at an easily accessible point in the cracked gas stream between the pyrolysis furnace and the cooler by arranging at said point a screen or sieve medium. Surprisingly, the formation of coke crusts now concentrates on this sieve medium and no longer occurs on the parts of the pyrolysis plant arranged behind the sieve medium, as seen in the direction of flow of the cracked gas stream.

The sieve medium of this invention may consist of a hollow structure of wire mesh or a structure consisting of several wire mesh disks. It is also possible to use irregularly joined filaments or even filament balls. Other materials may also be used in place of wire, e.g. ceramic bars or ceramic splinters as packing combined in a wide-meshed flat two-or three-dimensionally extended sieve medium. According to this invention anyone skilled in the art may manufacture a sieve medium such that it presents as large a surface as possible to the cracked gas stream and yet allows said gasstream to pass through.

A particularly advantageous embodiment of the sieve medium has been that of the wire mesh cage with its wall being more or less fitted to the cooler inlet head.

Another embodiment of this invention consists of several wire mesh cages fitted into each other, with the cage meshes increasing in size from the outer to the inner cages. A double cage, wherein the inner cage has wider meshes than the outer cage, is of particular advantage.

According to this invention the sieve medium is removed from the plant as soon as coke crust formations noticeably impede the flow of the cracked gas stream, and is replaced by a new coke-free sieve medium. According to this invention means for opening and closing have therefore been arranged at the point inside the pyrolysis plant where the sieve medium is placed.

The invention is illustrated by the following special example, without limiting the scope thereof.

This example is shown in the FIGURE. The cooler inlet head 1 is attached to the tube sheet, 2 by flange or connecting means not shown. The screen cage 4 stands on feet 3 on said tube sheet 2. Bars 5 are fixed within the cage 4 holding a plate cone 6. The cage 4 is upwardly tapered ending in an inlet nozzle 7. Said inlet nozzle 7 may be sealed to the inlet pipe or conduit 8 of said cooler inlet head 1 by means not shown. Inlet pipe 8 is flanged or disconnectably attached to inlet head 1 by a conventional disconnectable flange 12. The cage 4 consists of iron wire mesh with meshes of 6mm width and a wire thickness of 2mm. Said cage is reinforced by steel rings and steel bands, which are not shown in the FIGURE. The arrows indicate the approximate directions of the cracked gas stream. A major portion of the cracked gas that leaves hydrocarbon pyrolysis furnace 10, enters via inlet pipe 8 and inlet nozzle 7 into the cage 4 which cage 4 comprises an inner truncated cone 4a fitted upon an outer truncated cone 4b, each cone having different opening angles, passes through the cage meshes of the cage inner cone 4a into the space 9 intermediate the cage 4 and the cooler inlet head 1, and from there this major portion of cracked gas returns into the cage 4 and finally leaves the cage outer cone 4b via the bottom meshes to pass through the cooler 11, which latter is shown in the bottom of the FIGURE. Flanges 12 detachably connect inlet pipe or conduit 8 to cooler inlet head 1, and flanges 13 detachably connect the inlet head 1 to the cooler 11. Of the coke crusts formed on the wire occasionally larger pieces come off from the upper part of the cage 4 and fall to the bottom of said cage. In order to prevent these pieces from impeding the gas flow too strongly, the plate cone 6 has been provided for breaking the falling pieces. The embodiment as shown in this example was applied in an ethane pyrolysis plant. The cracked gases leaving the pyrolysis furnace 10 contain approximately 33 mole-percent of ethene and have a temperature of 800 i 50C. when entering the inlet pipe 8 of the cooler inlet head 1. When no sieve cage 4 was used, the plant had to be closed down about every three weeks because of coke obstructions. When it was used how- .ever, the only thing to do was to replace after 3 months the used cage by another coke-free one.

We claim:

1. The method of preventing coke obstruction in a system which includes a pyrolysis furnace for hydrocarbons, a connecting conduit, and a cooler, said furnace 3 4 being in sequence with the conduit and cooler, the 3. A method as recited in claim 2 wherein the second method comprising, method step comprises,

a. passing the effluent of the pyrolysis furnace at coke a i the effl e t out of the upper sides of the forming conditions into Sieve Cage having conical sieve cage for removing another portion of tom wall, 5 any coke formed.

guiding effluent out of the Sieve cage with a 4. A method as recited in claim 3 wherein the third flector,

c. passing the effluent back into the sieve cage, and

d. passing the effluent back out of the sieve cage for effecting occlusion of coke by filteration in said sieve cage prior to passing said effluent through said cooler.

2. A method as recited in claim 1 wherein the first method step comprises,

a. passing the effluent back into the lower sides of the conical sieve cage for removing a further portion of any coke formed.

5. A method as recited in claim 4 wherein the fourth method step comprises,

method Step comprises a. passing the effluent out of the bottom wall of the a. passing the effluent of the pyrolysis furnace at coke Sieve cage for effcting l Occlusion of Coke in forming conditions into an open upper small end of 531d S16v6 age P O o passing the effluent to the a conical sieve cage for removing a portion of any cooler. coke formed. 

1. THE METHOD OF PREVENTING COKE OBSTRUCTION IN A SYSTEM WHICH INCLUDES A PYROLYSIS FURNACE FOR HYDROCARBONS, A CONNECTING CONDUIT, AND A COOLER, SAID FURNACE BEING IN SEQUENCE WITH THE CONDUIT AND COOLER, THE METHOD COMPRISING, A. PASSING THE EFFLUENT OF THE PYROLYSIS FURNACE AT COKE FORMING CONDITIONS INTO A SIEVE CAGE HAVING A BOTTOM WALL, B. GUIDING THE EFFLUENT OUT OF THE SIEVE CAGE WITH A DEFLECTOR, C. PASSING THE EFFLUENT BACK INTO THE SIEVE CAGE, AND
 2. A method as recited in claim 1 wherein the first method step comprises, a. passing the effluent of the pyrolysis furnace at coke forming conditions into an open upper small end of a conical sieve cage for removing a portion of any coke formed.
 3. A method as recited in claim 2 wherein the second method step comprises, a. passing the effluent out of the upper sides of the conical sieve cage for removing another portion of any coke formed.
 4. A method as recited in claim 3 wherein the third method step comprises, a. passing the effluent back into the lower sides of the conical sieve cage for removing a further portion of any coke formed.
 5. A method as recited in claim 4 wherein the fourth method step comprises, a. passing the effluent out of the bottom wall of the sieve cage for effecting final occlusion of coke in said sieve cage prior to passing the effluent to the cooler. 